react-testing-library

Simple and complete React DOM testing utilities that encourage good testing practices.

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The problem

You want to write maintainable tests for your React components. As a part of
this goal, you want your tests to avoid including implementation details of your
components and rather focus on making your tests give you the confidence for
which they are intended. As part of this, you want your testbase to be
maintainable in the long run so refactors of your components (changes to
implementation but not functionality) don't break your tests and slow you and
your team down.

This solution

The react-testing-library is a very light-weight solution for testing React
components. It provides light utility functions on top of react-dom and
react-dom/test-utils, in a way that encourages better testing practices. Its
primary guiding principle is:

[The more your tests resemble the way your software is used, the more
confidence they can give you.][guiding-principle]

Example

// __tests__/fetch.js
import React from 'react'
import {render, fireEvent, cleanup, waitForElement} from 'react-testing-library'
// this adds custom jest matchers from jest-dom
import 'jest-dom/extend-expect'

// the mock lives in a __mocks__ directory
// to know more about manual mocks, access: https://jestjs.io/docs/en/manual-mocks
import axiosMock from 'axios'
import Fetch from '../fetch' // see the tests for a full implementation

// automatically unmount and cleanup DOM after the test is finished.
afterEach(cleanup)

test('Fetch makes an API call and displays the greeting when load-greeting is clicked', async () => {
  // Arrange
  axiosMock.get.mockResolvedValueOnce({data: {greeting: 'hello there'}})
  const url = '/greeting'
  const {getByText, getByTestId, container, asFragment} = render(
    <Fetch url={url} />,
  )

  // Act
  fireEvent.click(getByText(/load greeting/i))

  // Let's wait until our mocked `get` request promise resolves and
  // the component calls setState and re-renders.
  // getByTestId throws an error if it cannot find an element with the given ID
  // and waitForElement will wait until the callback doesn't throw an error
  const greetingTextNode = await waitForElement(() =>
    getByTestId('greeting-text'),
  )

  // Assert
  expect(axiosMock.get).toHaveBeenCalledTimes(1)
  expect(axiosMock.get).toHaveBeenCalledWith(url)
  expect(getByTestId('greeting-text')).toHaveTextContent('hello there')
  expect(getByTestId('ok-button')).toHaveAttribute('disabled')
  // snapshots work great with regular DOM nodes!
  expect(container.firstChild).toMatchSnapshot()
  // you can also use get a `DocumentFragment`, which is useful if you want to compare nodes across render
  expect(asFragment()).toMatchSnapshot()
})

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